Signal processing device and error correction method

ABSTRACT

Provided is a signal processing device including a signal receiving unit for receiving a multilevel signal having a signal waveform that is obtained by synchronously adding an encoded signal generated based on a specific coding rule and a clock which has an amplitude larger than the encoded signal and for which the transmission speed is half that of the encoded signal, an amplitude level detection unit for detecting an amplitude level of the multilevel signal received by the signal receiving unit, a violation detection unit for detecting a bit position at which rule violation of the specific coding rule occurred, based on a change pattern of the amplitude level detected by the amplitude level detection unit, and an error correction unit for correcting a detection value of the amplitude level corresponding to the bit position detected by the violation detection unit so that the rule violation is resolved.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a signal processing device, and anerror correction method.

2. Description of the Related Art

Most information processing apparatuses such as mobile phone andnotebook personal computer (hereinafter, a notebook PC) use a movablemember for a hinge portion connecting a main body to be operated by auser and a display portion on which information is displayed. However, alarge number of signal lines and power lines pass through the hingeportion, and a method for maintaining reliability of the wiring isdesired. Reducing the number of the signal lines passing through thehinge portion comes first to mind. Therefore, data transmissionprocessing between the main body and the display portion is made to beperformed by using a serial transmission method instead of a paralleltransmission method. When the serial transmission method is used, thenumber of signal lines is decreased, and furthermore, an effect that theelectromagnetic interference (EMI) is decreased can be also obtained.

In the serial transmission method, data is encoded and then transmitted.At that time, for example, a Non Return to Zero (NRZ) encoding scheme, aManchester encoding scheme, an Alternate Mark Inversion (AMI) encodingscheme, or the like is used as the encoding scheme. For example,JP-A-1991-109843 discloses a technology for transmitting data by usingan AMI code, which is a representative example of a bipolar code. Thepatent document also discloses a technology according to which a dataclock is transmitted after being expressed by an intermediate value of asignal level, and the receiving side regenerates the data clock based onthe signal level.

SUMMARY OF THE INVENTION

However, in an information processing apparatus such as a notebook PC,even if the serial transmission method using the above code is used, thenumber of signal lines wired in the hinge portion is still large. Forexample, in a case of a notebook PC, there are wiring lines related toan LED backlight for illuminating an LCD in addition to video signals tobe transmitted to the display portion, and thus several tens of signallines including these signal lines are wired in the hinge portion. TheLCD is an abbreviation for Liquid Crystal Display, and the LED is anabbreviation for Light Emitting Diode.

Therefore, the inventor of the present invention has developed anencoding scheme (hereinafter, new scheme) according to which a DCcomponent is not included and according to which a clock component canbe easily extracted from a received signal. Since a transmission signalgenerated based on this new scheme does not include a DC component, itcan be transmitted by being superimposed on DC power. Furthermore, bydetecting the polarity inversion cycle of the transmission signal, aclock can be regenerated by the receiving side without using a PLL.Therefore, a plurality of signal lines can be bound together, andthereby the number of signal lines can be reduced and also the powerconsumption and the circuit scale can be reduced. The PLL is anabbreviation for Phase Locked Loop.

However, the transmission signal generated based on the above-describednew scheme is a multilevel signal expressing one bit value in aplurality of amplitude levels. Thus, a SN ratio has to be about 10 dBhigher than that of a generally used 2-level signal expressing one bitvalue in one amplitude level. The above-described new scheme isdeveloped to be used for a transmission signal within a device. Thus, atransmission line to which the above-described new scheme is to beapplied is significantly higher in transmission quality compared to aradio channel. However, since the transmission signal will have multiplelevels, a transmission error may occur under the influence of unexpectedexternal noise, noise occurring within the device, and the like.

To improve the transmission quality of the transmission line,transmission data can be transmitted with an error correction code suchas a convolutional code added thereto, and the receiving side canperform the error correction. However, as described above, the newscheme assumes a transmission line with relatively high transmissionquality. Therefore, it would be excessive to perform a high-level errorcorrection using a convolutional code or the like on a minortransmission error occurring in such transmission line, and also, it isundesirable from the standpoint of the power consumption and circuitscale.

In light of the foregoing, it is desirable to provide a signalprocessing device and an error correction method which are novel andimproved, and which are capable of improving transmission quality in anenvironment where the transmission quality is relatively high withoutadding a special error correction code to transmission data.

According to an embodiment of the present invention, there is provided asignal processing device which includes a signal receiving unit forreceiving a multilevel signal having a signal waveform that is obtainedby synchronously adding an encoded signal generated based on a specificcoding rule and a clock which has an amplitude larger than the encodedsignal and for which the transmission speed is half that of the encodedsignal, an amplitude level detection unit for detecting an amplitudelevel of the multilevel signal received by the signal receiving unit, aviolation detection unit for detecting a bit position at which ruleviolation of the specific coding rule occurred, based on a changepattern of the amplitude level detected by the amplitude level detectionunit, and an error correction unit for correcting a detection value ofthe amplitude level corresponding to the bit position detected by theviolation detection unit so that the rule violation is resolved.

Furthermore, the error correction unit may be configured to correct thedetection value of the amplitude level corresponding to the bit positiondetected by the violation detection unit to an amplitude level adjacentto the detection value so that the rule violation is resolved.

Furthermore, the multilevel signal may have a signal waveform that isobtained by synchronously adding an encoded signal generated based on aspecific bipolar coding rule and the clock.

Furthermore, the signal receiving unit may be configured to receive amultilevel signal having a signal waveform which has six amplitudelevels (A3, A2, A1, −A1, −A2, −A3; |A3|>|A2|>|A1|) and which is obtainedby synchronously adding an encoded signal generated based on an AMIcoding rule and the clock. In this case, the violation detection unitrecognizes a change pattern of amplitude levels of consecutive two bitschanging from A3 to −A1 or from A1 to −A3 among amplitude levelsdetected by the amplitude level detection unit from the multilevelsignal received by the signal receiving unit, and detects the recognizedbit position as a bit position at which the rule violation occurred.

Furthermore, the error correction unit may be configured to correct, incase a change pattern of changing from A3 to −A1 is recognized by theviolation detection unit, the detection value A3 of the amplitude levelcorresponding to the recognized bit position to A2 or corrects thedetection value −A1 of the amplitude level to −A2. In this case, in casea change pattern of changing from A1 to −A3 is recognized by theviolation detection unit, the detection value A1 of the amplitude levelcorresponding to the recognized bit position is corrected to A2 or thedetection value −A3 of the amplitude level is corrected to −A2.

Furthermore, the signal processing device may further include a decodingunit for decoding a bit sequence based on an amplitude level which hasbeen corrected by the error correction unit, and an error detection unitfor performing error detection by using the bit sequence that has beendecoded by the decoding unit. In this case, in case a plurality ofcorrection candidates exist for the detection value of the amplitudelevel at the error correction unit, a bit sequence is decoded for eachcorrection candidate by the decoding unit, and a correct bit sequence isoutput by performing error detection by the error detection unit foreach decoding result.

According to another embodiment of the present invention, there isprovided an error correction method which includes the steps ofreceiving a multilevel signal having a signal waveform that is obtainedby synchronously adding an encoded signal generated based on a specificcoding rule and a clock which has an amplitude larger than the encodedsignal and for which the transmission speed is half that of the encodedsignal, detecting an amplitude level of the multilevel signal receivedin the step of receiving a signal, detecting a bit position at whichrule violation of the specific coding rule occurred, based on a changepattern of the amplitude level detected in the step of detecting anamplitude level, and correcting a detection value of the amplitude levelcorresponding to the bit position detected in the step of detecting aviolation so that the rule violation is resolved.

According to the embodiments of the present invention described above,transmission quality can be improved in an environment where thetransmission quality is relatively high without adding a special errorcorrection code to transmission data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram showing a configuration example of amobile terminal adopting a parallel transmission scheme;

FIG. 2 is an explanatory diagram showing a configuration example of amobile terminal adopting a serial transmission scheme;

FIG. 3 is an explanatory diagram showing a functional configurationexample of a mobile terminal adopting a general serial transmissionscheme;

FIG. 4 is an explanatory diagram showing a signal waveform of an AMIcode;

FIG. 5 is an explanatory diagram showing a functional configurationexample of a mobile terminal according to a new scheme;

FIG. 6 is an explanatory diagram showing an example of a transmissionsignal (multilevel code) generation method and an amplitudedetermination method according to the new scheme;

FIG. 7 is an explanatory diagram showing an example of an ideal eyepattern of a multilevel code (six levels);

FIG. 8 is an explanatory diagram showing a correspondence relationshipbetween a coding rule for the AMI code and an amplitude change patternfor a multilevel code for which the AMI code serves as a base;

FIG. 9 is an explanatory diagram showing a concept of an error detectionmethod according to an embodiment of the present invention;

FIG. 10 is an explanatory diagram showing an example of an eye patternof a multilevel code that is observed at the receiving side;

FIG. 11 is an explanatory diagram showing an example of a framestructure of a transmission frame;

FIG. 12 is an explanatory diagram showing a functional configurationexample of a mobile terminal according to the present embodiment;

FIG. 13 is an explanatory diagram showing an example of an errorcorrection method according to the present embodiment;

FIG. 14 is an explanatory diagram showing a functional configurationexample of a mobile terminal according to a modified example of thepresent embodiment; and

FIG. 15 is an explanatory diagram showing an example of an errorcorrection method according to a modified example of the presentembodiment.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the appended drawings. Note that,in this specification and the appended drawings, structural elementsthat have substantially the same function and structure are denoted withthe same reference numerals, and repeated explanation of thesestructural elements is omitted.

<Flow of Description>

The flow of a description of an embodiment of the present inventiondescribed below will be briefly mentioned. First, a device configurationof a mobile terminal 100 adopting a parallel transmission scheme will bedescribed with reference to FIG. 1. Herein, a demerit relating to theparallel transmission scheme will be pointed out. Then, a deviceconfiguration of a mobile terminal 130 adopting a serial transmissionscheme will be described with reference to FIG. 2. Then, a functionalconfiguration of a general mobile terminal 130 will be described withreference to FIG. 3. Herein, a brief description of an AMI code will bemade with reference to FIG. 4. The AMI is an abbreviation for AlternateMark Inversion.

Next, a functional configuration of a mobile terminal 130 adopting anencoding method according to the above-described new scheme will bedescribed with reference to FIG. 5. Then, an encoding method accordingto the above-described new scheme will be described with reference toFIG. 6. Then, a relationship between an amplitude level of a line codegenerated based on the above-described new scheme and an AMI coding rulewill be described with reference to FIGS. 7 and 8. Then, with referenceto FIGS. 8 to 11, a transmission error occurring in a transmission linein case of transmitting the line code according to the new scheme willbe described at the same time as describing a detection method for thetransmission error.

Next, a functional configuration of a mobile terminal 200 according toan embodiment of the present invention will be described with referenceto FIG. 12. Herein, an error correction method according to theembodiment will be described with reference to FIG. 13. Then, afunctional configuration of a mobile terminal 200 according to amodified example of the embodiment will be described with reference toFIG. 14. Herein, an error correction method according to the modifiedexample of the embodiment will be described with reference to FIG. 15.Lastly, the technical idea of the embodiment will be summarized andoperational effects obtained by the technical idea will be brieflydescribed.

(Description Items)

1: Introduction

1-1: Configuration of Mobile Terminal 100 Adopting Parallel TransmissionScheme

1-2: Configuration of Mobile Terminal 130 Adopting Serial TransmissionScheme

1-3: Functional Configuration of Mobile Terminal 130 according to NewScheme

2: Embodiment

2-1: AMI Coding Rule and Amplitude Pattern of Multilevel Code

2-2: Error Detection Method

2-3: Functional Configuration of Mobile Terminal 200

2-4: Error Correction Method

3: Modified Example

3-1: Functional Configuration of Mobile Terminal 200

4: Conclusion

1: Introduction

First, before describing in detail the technology according to anembodiment of the present invention, issues to be solved by the presentembodiment will be briefly summarized.

(1-1: Configuration of Mobile Terminal 100 Adopting ParallelTransmission Scheme)

First, a device configuration of a mobile terminal 100 adopting aparallel transmission scheme will be briefly described with reference toFIG. 1. FIG. 1 is an explanatory diagram showing an example of thedevice configuration of the mobile terminal 100 adopting a paralleltransmission scheme. In FIG. 1, a mobile phone is schematicallyillustrated as an example of the mobile terminal 100. However, theapplication scope of the technology described below is not limited to amobile phone. For example, it can be applied to an informationprocessing apparatus such as a notebook PC or various portableelectronic devices.

As shown in FIG. 1, the mobile terminal 100 mainly includes a displayunit 102, a liquid crystal unit 104 (LCD), a connecting unit 106, anoperation unit 108, a baseband processor 110 (BBP), and a parallelsignal path 112. The LCD is an abbreviation for Liquid Crystal Display.Additionally, the display unit 102 and the operation unit 108 may berespectively referred to as a display side and a main body side.Additionally, for the sake of explanation, a case where an image signalis transmitted through the parallel signal path 112 will be described asan example. Of course, the type of a signal to be transmitted throughthe parallel signal path 112 is not limited to such, and it may also bea control signal, an audio signal, or the like, for example.

As shown in FIG. 1, the liquid crystal unit 104 is provided on thedisplay unit 102. The image signal transmitted through the parallelsignal path 112 is input to the liquid crystal unit 104. The liquidcrystal unit 104 displays an image based on the input image signal.Also, the connecting unit 106 is a member connecting the display unit102 and the operation unit 108. The connecting member forming theconnecting unit 106 has a structure that enables the display unit 102 torotate 180 degrees in a Z-Y plane, for example. The connecting membercan also be formed such that the display unit 102 can rotate in an X-Zplane. In this case, the mobile terminal 100 will have a structurecapable of folding. Additionally, the connecting member may also have astructure that allows the display unit 102 to move freely in anydirection.

The baseband processor 110 is a computational processing unit thatprovides the mobile terminal 100 with a communication control functionand an application execution function. A parallel signal that is outputfrom the baseband processor 110 is transmitted through the parallelsignal path 112 to the liquid crystal unit 104 of the display unit 102.The parallel signal path 112 is provided with a plurality of signallines. In the case of a mobile phone, for example, the number n of thesignal lines is approximately fifty lines. The image signal transmissionspeed is approximately 130 Mbps in a case where the resolution of theliquid crystal unit 104 is QVGA. The parallel signal path 112 is wiredsuch that the lines pass through the connecting unit 106.

In other words, the plurality of signal lines that form the parallelsignal path 112 are provided in the connecting unit 106. As describedabove, if the range of movement of the connecting unit 106 is increased,the risk increases that the movement will inflict damage on the parallelsignal path 112. This would result in impairment of the reliability ofthe parallel signal path 112. On the other hand, if the reliability ofthe parallel signal path 112 is maintained, the range of movement of theconnecting unit 106 will be restricted. It is for this reason that theserial transmission scheme has come to be widely used in mobile phonesand the like in order to maintain the reliability of the parallel signalpath 112 while also increasing the degree of freedom of the movablemember that forms the connecting unit 106. The shift to the serialtransmission scheme for the transmission line is also being promotedfrom the standpoint of electromagnetic interference (EMI).

(1-2: Configuration of Mobile Terminal 130 Adopting Serial TransmissionScheme)

Now, a device configuration of a mobile terminal 130 adopting the serialtransmission scheme will be briefly described with reference to FIG. 2.FIG. 2 is an explanatory diagram showing an example of the deviceconfiguration of the mobile terminal 130 adopting the serialtransmission scheme. In FIG. 2, a mobile phone is schematicallyillustrated as an example of the mobile terminal 130. However, theapplication scope of the technology described below is not limited to amobile phone. For example, it can be applied to an informationprocessing apparatus such as a notebook PC or various portableelectronic devices. Furthermore, structural elements having functionssubstantially the same as those of the mobile terminal 100 of theparallel transmission scheme shown in FIG. 1 will be denoted with thesame reference numerals, and detailed explanation of these structuralelements will be omitted.

As shown in FIG. 2, the mobile terminal 130 mainly includes the displayunit 102, the liquid crystal unit 104 (LCD), the connecting unit 106,and the operation unit 108. Also, the mobile terminal 130 includes thebaseband processor 110 (BBP), parallel signal paths 132, 140, aserializer 134, a serial signal path 136, and a deserializer 138.

Unlike the mobile terminal 100 that is described above, the mobileterminal 130 transmits the image signal by the serial transmissionscheme through the serial signal path 136 that is wired through theconnecting unit 106. Therefore, the serializer 134 is provided in theoperation unit 108 to serialize the parallel signal that is output fromthe baseband processor 110. On the other hand, the deserializer 138 isprovided in the display unit 102 to parallelize the serial signal thatis transmitted through the serial signal path 136.

The serializer 134 converts the parallel signal that is output from thebaseband processor 110 and input through the parallel signal path 132into a serial signal. The serial signal that has been converted by theserializer 134 is input to the deserializer 138 through the serialsignal path 136. When the serial signal is input, the deserializer 138restores the original parallel signal from the input serial signal.Then, the deserializer 138 inputs the parallel signal to the liquidcrystal unit 104 through the parallel signal path 140.

In the serial signal path 136, a data signal that is encoded by the NRZencoding scheme, for example, may be transmitted on its own, oralternatively, the data signal and a clock signal may be transmittedtogether. The number k of the lines in the serial signal path 136 issignificantly less than the number n of the lines in the parallel signalpath 112 in the mobile terminal 100 in FIG. 1 (1≦k<<n). For example, thenumber k of the lines can be reduced to only a few lines. Therefore, thedegree of freedom relating to the movable range of the connecting unit106 through which the serial signal path 136 passes can be said to bevery much greater than that of the connecting unit 106 through which theparallel signal path 112 passes. At the same time, it can also be saidthat the reliability of the serial signal path 136 is high.Additionally, a differential signal such as a LVDS or the like isordinarily used for the serial signal that flows through the serialsignal path 136. The LVDS is an abbreviation for Low VoltageDifferential Signal.

Heretofore, the device configuration of the mobile terminal 130 has beenbriefly described. The overall device configuration of the mobileterminal 130 adopting the serial transmission scheme is approximately asdescribed above. However, how much the number of signal lines in theconnecting unit 106 can be reduced depends on the form of the signalflowing through the serial signal path 136. The serializer 134 and thedeserializer 138 are to determine the form of this signal. In thefollowing, functional configurations of the serializer 134 and thedeserializer 138 in a general serial transmission scheme will be brieflydescribed. Afterwards, functional configurations of the serializer 134and the deserializer 138 according to the above-described new schemewill be described.

(General Configuration)

Here, a functional configuration of the mobile terminal 130 adopting ageneral serial transmission scheme will be described with reference toFIG. 3. FIG. 3 is an explanatory diagram showing a functionalconfiguration example of the mobile terminal 130 adopting a generalserial transmission scheme. However, it should be noted that FIG. 3 isan explanatory diagram mainly illustrating the functional configurationsof the serializer 134 and the deserializer 138, and that description ofother structural elements are omitted.

(Serializer 134)

As shown in FIG. 3, the serializer 134 includes a P/S conversion unit152, an encoder 154, an LVDS driver 156, a PLL unit 158, and a timingcontrol unit 160.

As shown in FIG. 3, the parallel signal (P-DATA) and a parallel signalclock (P-CLK) are input from the baseband processor 110 to theserializer 134. The parallel signal that is input to the serializer 134is converted into a serial signal by the P/S conversion unit 152. Theserial signal that has been converted by the P/S conversion unit 152 isinput to the encoder 154. The encoder 154 adds a header and the like tothe serial signal and inputs it to the LVDS driver 156. The LVDS driver156 transmits the input serial signal to the deserializer 138 by adifferential transmission scheme according to LVDS.

In contrast, the parallel signal clock that is input to the serializer134 is input to the PLL unit 158. The PLL unit 158 generates a serialsignal clock from the parallel signal clock and inputs it to the P/Sconversion unit 152 and to the timing control unit 160. The timingcontrol unit 160 controls the timing of the transmission of the serialsignal by the encoder 154, based on the serial signal clock that isinput.

(Deserializer 138)

Furthermore, as shown in FIG. 3, the deserializer 138 mainly includes anLVDS receiver 172, a decoder 174, an S/P conversion unit 176, a clockregeneration unit 178, a PLL unit 180, and a timing control unit 182.

As shown in FIG. 3, the serial signal is transmitted to the deserializer138 from the serializer 134 by the differential transmission schemeaccording to LVDS. The serial signal is received by the LVDS receiver172. The serial signal that is received by the LVDS receiver 172 isinput to the decoder 174 and to the clock regeneration unit 178. Thedecoder 174 detects the beginning portion of the data by referring tothe header of the input serial signal and inputs the signal to the S/Pconversion unit 176. The S/P conversion unit 176 converts the inputserial signal into the parallel signal (P-DATA). The parallel signalthat has been converted by the S/P conversion unit 176 is output to theliquid crystal unit 104.

For its part, the clock regeneration unit 178 uses the built-in PLL unit180 to regenerate the parallel signal clock from the serial signal clockby referring to a reference clock (Ref.CLK) that is input from theoutside. The parallel signal clock that has been regenerated by theclock regeneration unit 178 is input to the decoder 174 and to thetiming control unit 182. The timing control unit 182 controls thereceiving timing based on the parallel signal clock that is input fromthe clock regeneration unit 178. The parallel signal clock (P-CLK) thatis input to the timing control unit 182 is output to the liquid crystalunit 104.

In this manner, the parallel signal (P-DATA) and the parallel signalclock (P-CLK) that are input to the serializer 134 from the basebandprocessor 110 are converted into the serial signals and are transmittedto the deserializer 138. The input serial signals are then restored bythe deserializer 138 to the original parallel signal and parallel signalclock. The parallel signal and the parallel signal clock that have beenrestored are input to the liquid crystal unit 104. In case the parallelsignal is an image signal, an image is displayed by the liquid crystalunit 104 based on the input parallel signal.

Heretofore, a general functional configuration of the mobile terminal130 adopting the serial transmission scheme has been described. Asdescribed above, the transmission line is serialized by converting theparallel signal into the serial signal and transmitting the serialsignal. The range of movement of the portion through which the serialsignal path passes is enlarged as a result, and the degree of freedom inthe disposition of the display unit 102 is increased. Therefore, in acase where the mobile terminal 130 is used to watch and listen to atelevision broadcast or the like, for example, it is possible totransform the mobile terminal 130 such that the display unit 102 isdisposed in a landscape orientation from the user's point of view. Theincrease in the degree of freedom brings with it a wider range of usesfor the mobile terminal 130, such that, in the addition of various typesof communication terminal functions, a wide variety of uses becomespossible, such as watching videos, listening to music, and the like.

Additionally, the above example describes a method of serializing a datasignal such as an image signal and transmitting the same. In addition tothe transmission line for the data signal, at least a power line isprovided in the connecting unit 106 of the mobile terminal 130. Break inthe power line will cause a serious damage, and thus, it is extremelyimportant to improve its reliability. Also, the restriction imposed onthe range of movement of the connecting unit 106 greatly differs for acase where the number of the transmission lines is 1 and for a casewhere it is 2 or more. Thus, a scheme has been devised according towhich the data signal is transmitted being superimposed on a powersignal.

This scheme is for encoding the data signal into a code form that doesnot include a DC component, such as an AMI code (see FIG. 4) and aManchester code, and transmitting the data signal by superimposing thesame on a power signal. Using this method will enable to reduce thenumber of the transmission lines in the connecting unit 106 by thenumber of the power lines.

(Summary of Issues 1)

As explained above, a parallel transmission scheme like that of themobile terminal 100 that is described above is not well suited to freelychange the positional relationship of the operation unit 108 and thedisplay unit 102. Accordingly, a method has been proposed to provide theserializer 134 and the deserializer 138, as in the mobile terminal 130that is described above, to make serial transmission possible andincrease the range of movement of the display unit 102. Also, to furtherimprove the movability of the display unit 102, a scheme has beenproposed to superimpose a signal on the power line and transmit thesignal, by taking the advantage of the characteristics of a code notincluding a DC component.

However, as shown in FIG. 3, the PLL unit 180 (hereinafter, PLL) is usedin the mobile terminal 130 to regenerate the clock of a received serialsignal. This PLL is necessary to extract a clock from a signal which isencoded according to the Manchester encoding scheme or the like.However, the amount of power consumption of the PLL itself is not small.Thus, providing the PLL will increase the power consumption of themobile terminal 130 by the amount of the power consumption by the PLL.Such increase in the amount of the power consumption will be a graveissue for a small device such as a mobile phone and the like.

In view of such issue, the inventor of the present invention has deviseda novel transmission scheme (new scheme) of transmitting a signal whichdoes not include a DC component and which is transmitted by using a codefor which a PLL circuit is not necessary at the time of clockregeneration, so that a PLL will not be necessary at the deserializer138. Hereunder, this new scheme will be described. Additionally,although, in the following explanation, an encoding method according tothe new scheme for which the AMI code serves as a base will be taken asthe concrete example, the application target of the new scheme is notlimited to the AMI code.

(1-3: Functional Configuration of Mobile Terminal 130 according to NewScheme)

First, the AMI code will be briefly described, and then, the functionalconfiguration of the mobile terminal 130 according to the new scheme andthe encoding method of such mobile terminal 130 will be described.

(Signal Waveform of AMI Code)

First, the signal waveform of the AMI code and its characteristics willbe briefly described with reference to FIG. 4. FIG. 4 is an explanatorydiagram showing an example of the signal waveform of the AMI code. Inthe following explanation, it is assumed that A is any positive number.

The AMI code is a code that uses an electrical potential of zero toexpress a data value of zero and potentials of A and −A to express adata value of 1. Note, however, that the potential A and the potential−A are used alternately. That is, after a data value of 1 has beenexpressed by the potential A, if the next data bit is also a 1, that 1will be expressed by the potential −A. Because the data values areexpressed by repeatedly inverting the polarity in this manner, the AMIcode does not contain a DC component.

Other codes with the same type of characteristics as the AMI codeinclude, for example, the partial response scheme that expresses thedata as PR (1, −1), PR (1, 0, −1), PR (1, 0, . . . , −1), and the like.Transmission codes that use this sort of polarity inversion are calledbipolar codes. Alternatively, a dicoding scheme or the like can also beused for the encoding method of the new scheme. In the followingexplanation, an encoding method which uses an AMI code with a duty of100% will be described as an example.

FIG. 4 schematically shows the AMI code of periods T1 to T14. In thedrawing, a data value 1 appears at timings T2, T4, T5, T10, T11, T12,and T14. If the potential is A at timing T2, the potential at timing T4is −A. Also, the potential at timing T5 is A. As such, the amplitudecorresponding to the data value 1 is alternately inverted betweenpositive and negative values. This is the polarity inversion that isdescribed above.

In contrast, a data value 0 is expressed by a potential 0 at all times.This form of expression allows the AMI code to not include a DCcomponent. However, as can be seen at timings T6 to T9, it sometimesresults in consecutive potentials of 0. The consecutive potentials of 0make it difficult to extract the clock component from the signalwaveform without using a PLL. Accordingly, the inventor of the presentinvention has devised, as the new scheme, a method of superimposing aclock on the AMI code (or a code having equivalent characteristics)before transmitting the same. This method will be described later indetail.

(Functional Configuration of Mobile Terminal 130)

Hereunder, the functional configuration of the mobile terminal 130according to the new scheme will be described with reference to FIG. 5.FIG. 5 is an explanatory diagram showing an example of the functionalconfiguration of the mobile terminal 130 according to the new scheme.However, it should be noted that FIG. 5 is an explanatory diagram mainlyillustrating the functional configurations of the serializer 134 and thedeserializer 138, and that description of other structural elements areomitted. Also, detailed description of the structural elements of themobile terminal 130 already described are omitted.

(Serializer 134)

First, the serializer 134 will be described. As shown in FIG. 5, theserializer 134 is configured from the P/S conversion unit 152, the LVDSdriver 156, the PLL unit 158, the timing control unit 160, and anencoder 192. The main point of difference from the general configurationdescribed earlier is in the function of the encoder 192.

As shown in FIG. 5, the parallel signal (P-DATA) and the parallel signalclock (P-CLK) are input from the baseband processor 110 to theserializer 134. The parallel signal that is input to the serializer 134is converted into a serial signal by the P/S conversion unit 152. Theserial signal that has been converted by the P/S conversion unit 152 isinput to the encoder 192. The encoder 192 adds a header and the like tothe serial signal and generates a transmission frame (see FIG. 11).Furthermore, the encoder 192 encodes the generated transmission frame bythe encoding method of the new scheme described later, and generates atransmission signal.

Next, a method of generating the encoded signal by the encoder 192 willbe described with reference to FIG. 6. FIG. 6 is an explanatory diagramshowing an example of the encoding method of the new scheme.Additionally, FIG. 6 illustrates a method of generating a code for whichthe AMI code serves as a base. However, the new scheme is not limited tosuch, and it can be applied to any code having the same characteristicsas the AMI code. For example, it can be applied to a bipolar code, acode according to a partial response scheme, and the like.

The signal that is shown in (C) of FIG. 6 is a signal that has beenencoded by the encoding method of the new scheme. In this signal, datavalues 1 are expressed by a plurality of potentials A1 (−1, −3, 1, 3)and data values 0 are expressed by a plurality of potentials A2 (−2, 2)that are different from the potentials A1. Additionally, this signal isconfigured such that the polarities are inverted and also such that thesame potential does not occur consecutively. For example, referring tothe section where data values 0 occur consecutively in timings T6 to T9,the potentials are −2, 2, −2, 2. Using this sort of code makes itpossible to regenerate the clock component by detecting both the risingand the falling edges, even if the same data value occurs consecutively.

Because the encoder 192 generates a code as described above, it isprovided with an adder ADD. As shown in FIG. 6, the encoder 192, forexample, encodes a serial signal that is input into an AMI code (A), andinputs the AMI code to the adder ADD. Furthermore, the encoder 192generates a clock (B) having a frequency (2/Fb) half that of thetransmission speed Fb of the AMI code, and inputs the clock to the adderADD. Here, the amplitude of the clock is N times that of the AMI code(N>1; N=2 in the example in FIG. 6). The encoder 192 then adds the AMIcode and the clock by using the adder ADD, and generates a code (C). Atthis time, the AMI code and the clock are synchronously added with theiredges aligned.

The amplitude level of the code (C) obtained by synchronously adding theAMI code (A) and the clock (B) may take six values, i.e. 3, 2, 1, −1,−2, and −3, in the example showing in FIG. 6. That is, the transmissionsignal is a multilevel signal having six amplitude levels. Thus, theranges of the amplitude levels of the transmission signal become widercompared to a case of transmitting the AMI code (A) as it is, and thetransmission error becomes more likely to occur. This point will bedescribed later in detail. Additionally, a configuration ofsynchronously adding the AMI code (A) and the clock (B) has beendescribed here for the sake of simplicity of the explanation. However,the encoder 192 may be configured such that data is directly encodedinto the waveform of the code (C). For example, in the case of FIG. 6,data sequence 0, 1, 0, 1, 1, 0, . . . , 1 may be directly converted intoamplitude levels 2, −1, 2, −3, 3, −2, . . . , −1 by the encoder 192.

FIG. 5 will be again referred to. The serial signal that has beenencoded by the encoder 192 in the manner described above is input to theLVDS driver 156. The LVDS driver 156 transmits the input serial signalto the deserializer 138 by a differential transmission scheme accordingto LVDS. On the other hand, a parallel signal clock input to theserializer 134 is input to the PLL unit 158. The PLL unit 158 generatesa serial signal clock from the parallel signal clock, and inputs theserial signal clock to the P/S conversion unit 152 and the timingcontrol unit 160. The timing control unit 160 controls the timing of thetransmission of the serial signal by the encoder 192, based on the inputserial signal clock. As described above, a serial signal is encoded andtransmitted from the serializer 134 to the deserializer 138.

(Deserializer 138)

Next, the deserializer 138 will be described. As shown in FIG. 5, thedeserializer 138 is mainly configured from the LVDS receiver 172, theS/P conversion unit 176, the timing control unit 182, a clock detectionunit 196, and a decoder 194. The main point of difference from thegeneral configuration described above is in the presence of the clockdetection unit 196, which does not have a PLL.

As described above, the serial signal is transmitted from the serializer134 to the deserializer 138 by the differential transmission schemeaccording to LVDS. The serial signal is received by the LVDS receiver172. The serial signal received by the LVDS receiver 172 is input to thedecoder 194 and the clock detection unit 196. The decoder 194 detectsthe beginning portion of the data by referring to the header of theinput serial signal and decodes the serial signal that was encodedaccording to the encoding scheme used by the encoder 192.

Next, a method of decoding by the decoder 194 will be described byreferring again to FIG. 6. As described above, the serial signal isencoded by the encoder 192 into a signal waveform of the code (C) havingsix amplitude levels. Thus, the decoder 194 can decode the originalsignal by performing threshold determination of determining whether theamplitude level of the received signal is A1 or A2. For example, fourthreshold values (L1, L2, L3, L4) that are shown in (C) in FIG. 6 areused to distinguish between amplitude level A1 (−1, −3, 1, 3), whichcorresponds to data value 1, and amplitude level A2 (−2, 2), whichcorresponds to data value 0. The decoder 194 first compares theamplitude level of the input signal to the four threshold valuesdescribed above and determines whether the amplitude level is A1 or A2.Then, the decoder 194 decodes the original NRZ data based on thedetermination result and restores the serial signal that wastransmitted.

FIG. 5 will be again referred to. The serial signal that has beendecoded by the decoder 194 is input to the S/P conversion unit 176. TheS/P conversion unit 176 converts the input serial signal into theparallel signal (P-DATA). The parallel signal that has been converted bythe S/P conversion unit 176 is input to the liquid crystal unit 104. Incase the parallel signal is an image signal, an image is displayed bythe liquid crystal unit 104 based on the image signal.

Now, a clock becomes necessary to perform the above-described decodingprocess. Accordingly, the clock detection unit 196 detects the clockcomponent in the signal input from the LVDS receiver 172. As has alreadybeen explained, the code (C) in FIG. 6 is obtained by synchronouslyadding the code (A) and the clock (B). Thus, this code (C) has acharacteristic that the polarity is inverted every half cycle of theclock. When using this characteristic, the clock component is obtainedby comparing the amplitude level and threshold level L0 (potential 0)and detecting the polarity inversion cycle of the amplitude. As aresult, the clock detection unit 196 does not have to use a PLL at thetime of detecting the clock component. Accordingly, a PLL does not haveto be provided, and the power consumption and the circuit scale of thedeserializer 138 can be reduced to that extent.

Now, the clock component detected by the clock detection unit 196 isinput to the decoder 194 and the timing control unit 182. The clockcomponent input to the decoder 194 is used at the time of performing anNRZ data decoding process according to the amplitude level determinationfor a multilevel code. Furthermore, the timing control unit 182 controlsa reception timing based on the clock input from the clock detectionunit 196. The clock (P-CLK) input to the timing control unit 182 isoutput to the liquid crystal unit 104.

The threshold determination performed by the decoder 194 and the clockdetection unit 196 described above is realized by using a comparator,for example. The clock component is extracted at the clock detectionunit 196 from the output result of a comparator in which threshold valueis amplitude level 0. In contrast, the decoder 194 uses a comparatorwith four threshold levels, i.e. 2.5, 1.5, −1.5, and −2.5, to determinesix amplitude levels, i.e. 3, 2, 1, −1, −2, and −3, for example. Anamplitude level corresponding to each timing is determined based on theoutput results of these comparators. Also, the original NRZ data isdecoded based on the determination result.

As described above, using a code which does not include a DC componentand from which a clock component can be regenerated based on thepolarity inversion cycle allows the deserializer 138 to perform clockdetection without using a PLL, and thus, the power consumption of themobile terminal 130 can be greatly reduced. Additionally, theabove-described example illustrates a differential transmission schemeaccording to LVDS. However, a power superimposition scheme ofsuperimposing a multilevel signal on a DC power signal and transmittingthe same can also be used. According to this configuration, the range ofmovement of the connecting unit 106 can be further increased.

(Summary of Issues 2)

Heretofore, the functional configuration of the mobile terminal 130according to the new scheme and the encoding/decoding method have beendescribed. As described above, by using the encoding method according tothe new scheme, the number of lines in the connecting unit 106 isgreatly reduced, and also, significant effects such as the reduction inthe circuit scale and the power consumption amount can be obtained. Ashas been explained, the new scheme has been developed to be used forsignal transmission within a device. Such transmission line issignificantly higher in quality than a radio channel. However, atransmission signal generated according to the encoding method of thenew scheme is a multilevel signal expressing one bit value in aplurality of amplitude levels.

Accordingly, a SN ratio has to be about 10 dB higher than that of agenerally used 2-level transmission signal expressing one bit value inone amplitude level. As a result, a transmission error may occur underthe influence of unexpected external noise, noise occurring within thedevice, and the like. For example, the eye pattern of theabove-described multilevel signal for which the AMI code serves as abase will have a form as shown in FIG. 7. However, FIG. 7 schematicallyshows an ideal eye pattern at the time point of generation of amultilevel code, and in reality, the edge portion may be rounded at thetime of passing through a filter circuit having high-frequency cutoffcharacteristics, a transmission line or the like, or the waveform of theamplitude may be thick due to the noise in the transmission line or thelike, and thus the eye pattern will take a form as shown in FIG. 10.

In the waveform in FIG. 7, the six amplitude levels, 3, 2, 1, −1, −2,and −3, are distinctly divided at an interval of height 1. Also, eachamplitude level has a fixed width of 1/Fb. In case of such waveform, acorrect amplitude level can be obtained no matter at which position thethreshold determination of the amplitude level is performed as long asthe threshold determination is performed within the width 1/Fb. That is,if a received signal and a clock are correctly synchronized, a correctamplitude level will be detected as a result of threshold determinationbased on the clock. However, in case of a waveform as shown in FIG. 10,the amplitude level will be different depending on the position to besampled within the width 1/Fb corresponding to each amplitude level.

Also, as can be seen from the eye pattern in FIG. 10, the amplitudelevel itself has a width in the vertical axis direction. Thus, even ifan amplitude level at a position which is supposed to have the sameamplitude level is sampled, a different amplitude level is obtaineddepending on the timing of sampling. If the width is small, the resultof the threshold determination performed using a threshold level setaround the middle of each amplitude level will seldom indicate anotheramplitude level. However, if the width becomes large, a result ofthreshold determination might be different from the actual amplitudelevel.

The probability of such error occurring can be roughly estimated by theopening rate of an eye (for example, E1, E2) included in the eye patternas shown in FIG. 10. The opening rate here means the opening area of theeye in comparison to the opening area of the ideal eye pattern shown inFIG. 7, for example. That is, the opening rate of the eye of thewaveform shown in FIG. 7 is 100%. However, as shown in FIG. 10, theopening rate of each eye is normally reduced under the influence ofhigh-frequency cutoff or the influence of noise or the like. Also, thetransmission signal of the new scheme is a multilevel signal, and thus,the opening rate of the eye corresponding to a position at a highamplitude level is further greatly reduced.

For example, the opening rate of the eye E1 appearing between amplitudelevels 2 and 3 is lower than that of the eye E2 appearing betweenamplitude levels 1 and 2. Similarly, the opening rate of the eyeappearing between amplitude levels −2 and −3 is lower than that of theeye appearing between amplitude levels −1 and −2. Therefore, an errortends to occur in the threshold determination of amplitude levels 3 and−3. Similarly, an error is more likely to occur in a case of performingthe threshold determination of amplitude levels 2 and −2 than in a caseof determining amplitude levels 1 and −1. That is, the probability of anerror occurring in the threshold determination is higher in case oftransmitting the multilevel signal according to the new scheme than incase of transmitting, as it is, a transmission signal having thewaveform of the AMI code.

Accordingly, it is conceivable to perform an error correction to copewith a transmission error occurring in this manner. Normally, to improvetransmission quality, an error correction code such as a convolutionalcode is added to transmission data, and the receiving side performs theerror correction. However, a transmission line with relatively hightransmission quality is assumed, and it would be excessive to perform ahigh-level error correction using a convolutional code or the like on asmall transmission error occurring in such transmission line. Also, sucherror correction will increase the power consumption and the circuitscale, and therefore is not desirable. Thus, an error correction methodwhich is capable of improving the transmission quality without adding aspecial error correction code is desired.

2: Embodiment

The technology described below has been devised in view of the issues asdescribed above. Hereunder, an embodiment of the present invention willbe described. The present embodiment proposes an error correction methodwhich is capable of further improving the transmission quality withoutadding a special error correction code to transmission data in anenvironment where the transmission quality is relatively high. Morespecifically, a coding rule violation is detected from the pattern ofthe amplitude level obtained by threshold determination at the receivingside, and an error correction is performed so as to resolve the codingrule violation. Hereunder, a more detailed description will be givenwhile referring to a multilevel code for which the AMI code serves as abase as a concrete example.

(2-1: AMI Coding Rule and Amplitude Pattern of Multilevel Code)

First, a relationship between an AMI coding rule and the amplitudepattern of a multilevel code based on the AMI coding rule, and thecoding rule violation in the multilevel code will be described withreference to FIG. 8. FIG. 8 is an explanatory diagram for describing therelationship between the AMI coding rule and the amplitude pattern ofthe multilevel code based on the AMI coding rule, and for describing thecoding rule violation in the multilevel code.

FIG. 8 describes, in the form of a table, the amplitude level of an AMIcode (AMI data), the amplitude level of a clock (CLOCK) to besynchronously added to the AMI code, and the amplitude level of amultilevel code (final code). Additionally, the multilevel code (C) ofthe new scheme shown in FIG. 6 is generated from the AMI code (A) andthe clock (B) based on the coding rule shown in FIG. 8.

First, rows of AMI data 1 will be referred to. The rows of AMI data 1are associated with CLOCKs 2 and −2. Also, final code 3 is associatedwith CLOCK 2. Similarly, final code −1 is associated with CLOCK −2. Thisindicates that final code 3 is obtained as a result of adding CLOCK 2 toAMI data 1. Similarly, it is indicated that final code −1 is obtained asa result of adding CLOCK −2 to AMI data 1.

Next, rows of AMI data 0 will be referred to. The rows of AMI data 0 areassociated with CLOCKs 2 and −2. Also, final code 2 is associated withCLOCK 2. Similarly, final code −2 is associated with CLOCK −2. Thisindicates that final code 2 is obtained as a result of adding CLOCK 2 toAMI data 0. Similarly, it is indicated that final code −2 is obtained asa result of adding CLOCK −2 to AMI data 0.

Next, rows of AMI data −1 will be referred to. The rows of AMI data −1are associated with CLOCKs 2 and −2. Also, final code 1 is associatedwith CLOCK 2. Similarly, final code −3 is associated with CLOCK −2. Thisindicates that final code 1 is obtained as a result of adding CLOCK 2 toAMI data −1. Similarly, it is indicated that final code −3 is obtainedas a result of adding CLOCK −2 to AMI data −1.

The AMI coding rule will be again described for the sake ofclarification. The AMI coding rule is to express data value 1 byamplitude level 1 or −1, and to express data value 0 by amplitude level0. The characteristic of the AMI coding rule lies in that the amplitudelevel of the previously input data value 1 is referred to at the time ofencoding data value 1. Specifically, if the previously input data value1 was encoded to have amplitude level 1, the currently input data 1 willbe encoded to have amplitude level −1. Similarly, if the previouslyinput data 1 was encoded to have amplitude level −1, the currently inputdata 1 will be encoded to have amplitude level 1. Accordingly, anamplitude pattern with consecutive amplitude levels 1 or an amplitudepattern with consecutive amplitude levels −1 is not possible.

Such impossible amplitude patterns will be referred to as the codingrule violations. The AMI coding rule violation is as described above.Furthermore, the multilevel code of the new scheme for which the AMIcode serves as a base inherits the AMI coding rule. Accordingly, acoding rule violation based on the AMI coding rule violation also existsfor the multilevel code of the new scheme. As described above, accordingto the AMI coding rule, a pattern (1, 1) where amplitude levels 1 occurconsecutively is a coding rule violation. When a clock (2, −2) issynchronously added to this pattern of the AMI code, a pattern (3, −1)is obtained for a multilevel code. That is, a pattern (3, −1) is acoding rule violation for the multilevel code of the new scheme forwhich the AMI code serves as a base.

Similarly, according to the AMI coding rule, a pattern (−1, −1) whereamplitude levels −1 occur consecutively is a coding rule violation. Whena clock (2, −2) is synchronously added to this pattern of the AMI code,a pattern (1, −3) is obtained for a multilevel code. That is, a pattern(1, −3) is a coding rule violation for the multilevel code of the newscheme for which the AMI code serves as a base. Additionally, whentaking into consideration also a case of synchronously adding a clock(−2, 2), at least four patterns, (3, −1), (1, −3), (−1, 3) and (−3, 1)are coding rule violations relating to the above-described multilevelcode of the new scheme. It should be noted that there is also a patternwhere amplitude level 0 exists inbetween, such as a pattern (1, 0, 1),for the coding rule violation in the AMI code.

The coding rule violation as described above does not usually occurunless intended by the transmitting side. However, if the result of athreshold determination includes an error, the coding rule violation asdescribed above may occur. Accordingly, the present embodiment proposesa method of detecting a coding rule violation in the multilevel code asdescribed above at the receiving side and of performing error correctionso as to resolve the coding rule violation. However, as has already beenexplained, the transmission line assumed in the present embodiment issignificantly higher in transmission quality than a radio channel andthe like. Accordingly, it would be enough if an error of one bit or of aseveral bits in one transmission frame can be corrected. Thus, thepresent embodiment proposes a method of detecting the coding ruleviolation as illustrated in FIG. 8 and of performing error correctionaccording to the detection result.

As described above, a pattern such as a pattern (1, 0, 1) also existsfor the coding rule violation in the AMI code. To detect such pattern,information relating to the polarity (+/−) of the amplitude levelcorresponding to previously detected data 1 has to be held. Also, itbecomes necessary to determine at which timing of the pattern (1, 0, 1)the error occurred. If the results of the threshold determinationcorresponding to amplitude level 0 of the AMI code are numerous, theprocess of determining at which timing the error occurred becomescomplicated. As a result, the circuit scale and the power consumptionwill be increased.

Thus, the present embodiment does not aim for perfect error correctionbut aims to improve the transmission quality by correcting at least apart of the errors. For this reason, there is a merit that theapplication of the error correction method of the present embodimenthardly increases the circuit scale and the power consumption, and also,that it can be implemented relatively easily.

(2-2: Error Detection Method)

Here, the error detection method according to the present embodimentwill be described more concretely with reference to FIG. 9. FIG. 9schematically shows a received waveform which includes a code error. Thewaveform shown in FIG. 9 is that which is obtained at the receiving sidewhen the multilevel code (C) in FIG. 6 is transmitted. In this example,the amplitude level at timing T13 is affected by a noise or the like. Asshown in FIG. 6, the amplitude level at timing T13 is originally 2.However, in the example of FIG. 9, the amplitude level at timing T13 isbetween 2 and 3 and rather near to 3. Thus, when the thresholddetermination is performed, the amplitude level will be determined to be3.

Such erroneous determination makes the pattern of the amplitude levelsat timings T13 and T14 (3, −1). This amplitude pattern corresponds to acoding rule violation in the multilevel code as shown in FIG. 8.Accordingly, it is estimated based on the detection of this coding ruleviolation that an error has occurred at either timing T13 or T14.According to the present embodiment, an error is detected by using suchmethod, and the detected error is corrected. In the example of FIG. 9,an error is rectified by correcting either of the amplitude levels attimings T13 and T14.

As has been described, the transmission characteristics of thetransmission line assumed in the present embodiment is relatively good.Accordingly, a grave error of an amplitude level by two levels or morerarely occurs. Conversely, in a situation where such grave error occurs,a sufficient effect is not obtained by the error correction method ofthe present embodiment because the errors occur randomly and frequently.For this reason, the present embodiment takes into consideration only acorrection to an adjacent amplitude level. For example, in the exampleof FIG. 9, amplitude level 3 detected at timing T13 may be corrected toamplitude level 2. Also, amplitude level −1 detected at timing T14 maybe corrected to amplitude level −2. Additionally, the error correctionmethod according to the present embodiment will be described later indetail.

As described above, the error detection method according to the presentembodiment is based on the coding rule violation in a multilevel code.However, also in the present embodiment, data transmission is performedin many cases with a CRC (Cyclic Redundancy Check) added to atransmission frame as shown in FIG. 11. Accordingly, error detection canalso be additionally performed by the CRC. By using the error detectionby the CRC, whether the error correction by the present embodiment basedon the coding error violation is accurate or not can also be checked.These methods will be described later. Here, referring to FIG. 11, aframe structure of the transmission frame will be simply described.

FIG. 11 is an example of the frame structure used at the time oftransmitting data. This transmission frame F1 includes a synchronizationcode (SYNC) A1, data A2 and a CRC code A3. As will be described later,the transmission frame F1 is encoded into the multilevel code describedabove, and is transmitted as a multilevel signal. Additionally, thesynchronization code A1 is a specific synchronization pattern indicatingthe beginning position of the transmission frame A1. The data A2 istransmission target data. For example, when being used for anapplication for a mobile phone or the like, image data to be transmittedto the liquid crystal unit 104 and various control data for controllingthe display unit 102 will be included as the data A2. The CRC code A3 isused for the error detection for the data A2. Normally, a CRC code A3having a code length of about 16 bits or 32 bits is used.

(2-3: Functional Configuration of Mobile Terminal 200)

Next, the functional configuration of a mobile terminal 200 capable ofperforming the error detection method and the error correction methodaccording to the present embodiment will be described with reference toFIG. 12. FIG. 12 is an explanatory diagram showing a functionalconfiguration example of the mobile terminal 200 according to thepresent embodiment. Description of portions that are substantially thesame of those of the mobile terminal 130 of the new scheme shown in FIG.5 will be simplified or will be omitted.

As shown in FIG. 12, the mobile terminal 200 is mainly configured from atransmitting unit 202 and a receiving unit 204. Furthermore, thetransmitting unit 202 and the receiving unit 204 are connected by atransmission line 206. For example, a coaxial cable or a twisted paircable is used as the transmission line 206. In case of transmitting themultilevel signal described above with power superimposed thereon, acoaxial cable is used. Furthermore, the transmitting unit 202 is mainlyprovided with a SYNC adding unit 212, a CRC adding unit 214 and anencoding unit 216. Also, the receiving unit 204 is provided with adecoding unit 232, a SYNC detection unit 234, an error patterndetection/correction unit 236, and a CRC check unit 238.

First, 2-level transmission data (NRZ data) is input to the SYNC addingunit 212. When the transmission data is input, the SYNC adding unit 212adds a synchronization code to the transmission data. The transmissiondata to which the synchronization code has been added is input to theCRC adding unit 214. When the transmission data to which thesynchronization code has been added is input, the CRC adding unit 214adds a CRC code to the transmission data. A transmission frame having astructure as shown in FIG. 11 is generated by adding a synchronizationcode and a CRC code to transmission data in this manner. The generatedtransmission frame is input to the encoding unit 216.

When the transmission frame is input, the encoding unit 216 converts theinput transmission frame into an AMI code based on the AMI coding rule.Furthermore, the encoding unit 216 converts the AMI code into amultilevel code based on the coding rule shown in FIG. 8. That is, theencoding unit 216 generates a multilevel code waveform that is obtainedby synchronously adding a clock to an AMI code waveform. By generatingdata in a multilevel code from data in the AMI code based on the tableof FIG. 8 in this manner, it becomes unnecessary to actually performsignal processing of synchronously adding the signal waveform of the AMIcode and the signal waveform of the clock. That is, by modulating acarrier based on the data in the final code shown in FIG. 8, atransmission signal (multilevel signal) based on the multilevel code isgenerated. Of course, the multilevel signal may be generated bysynchronously adding, by signal processing, the clock signal and a datasignal based on the AMI code.

The multilevel signal obtained in this manner is transmitted to thereceiving unit 204 through the transmission line 206. When themultilevel signal reaches the receiving unit 204, it is first input tothe decoding unit 232. The decoding unit 232 performs the thresholddetermination by a comparator or the like and detects the amplitudelevel of the multilevel signal. Furthermore, the decoding unit 232decodes the 2-level transmission data from the data in the multilevelcode based on the detected amplitude level. At this time, the decodingunit 232 converts from the data in the multilevel code to the data inthe AMI code by using the coding rule shown in FIG. 8, decodes theobtained data in the AMI code based on the AMI coding rule, andgenerates 2-level data corresponding to the transmission frame. The2-level data generated at the decoding unit 232 (hereinafter, decodeddata) is input to the SYNC detection unit 234.

When the decoded data is input, the SYNC detection unit 234 detects thesynchronization code from the decoded data, and detects the beginningportion of the transmission frame. Then, the SYNC detection unit 234inputs to the decoding unit 232 the data and the CRC code following thesynchronization code. When the detection of the synchronization code bythe SYNC detection unit 234 is completed in this manner, the decodingunit 232 performs error correction on the input data. First, thedecoding unit 232 inputs the amplitude data of the multilevel code andthe decoded data to the error pattern detection/correction unit 236. Theerror pattern detection/correction unit 236 checks the amplitude patternof the multilevel code and detects the coding error violation. At thistime, the error pattern detection/correction unit 236 detects a portionwhere the amplitude pattern of consecutive two bits is any of (3, −1),(1, −3), (−1, 3) and (−3, 1).

When no coding rule violation is detected, the decoded data is input tothe CRC check unit 238 as it is. In contrast, if any of the amplitudepatterns mentioned above is detected, the error patterndetection/correction unit 236 corrects the decoded data based on acorrection rule shown in FIG. 13. For example, when a pattern (3, −1) isdetected, the error pattern detection/correction unit 236 presumes thatthe pattern of the correct amplitude level is (2, −1), and corrects thedecoded data of the corresponding bits to (0, 1). Similarly, when apattern (−1, 3) is detected, the error pattern detection/correction unit236 presumes that the pattern of the correct amplitude level is (−1, 2),and corrects the decoded data of the corresponding bits to (1, 0).

Furthermore, when a pattern (1, −3) is detected, the error patterndetection/correction unit 236 presumes that the pattern of the correctamplitude level is (1, −2), and corrects the decoded data of thecorresponding bits to (1, 0). Furthermore, when a pattern (−3, 1) isdetected, the error pattern detection/correction unit 236 presumes thatthe pattern of the correct amplitude level is (−2, 1), and corrects thedecoded data of the corresponding bits to (0, 1). The decoded datacorrected in this manner is input from the error patterndetection/correction unit 236 to the decoding unit 232.

The decoding unit 232 inputs the decoded data which has been correctedby the error pattern detection/correction unit 236 and the CRC code tothe CRC check unit 238. The CRC check unit 238 performs error check onthe decoded data based on the input CRC code. The error detection andthe error correction by the error pattern detection/correction unit 236are performed only to detect a bit having a high probability of being anerror and to correct a detected value. Thus, the CRC check is performedto check whether the decoded data after the error correction is trulycorrect. Additionally, whether the error correction by the error patterndetection/correction unit 236 is correct or incorrect can be checked bythe error detection performed by the CRC check unit 238. The decodeddata for which an error has been detected by the CRC check unit 238 isdiscarded, or is output, as it is, as received data.

The decoded data for which the error check has been performed by the CRCcheck unit 238 is output as received data to other structural elements.For example, when the transmitting unit 202 corresponds to theserializer 134 described above and the receiving unit 204 corresponds tothe deserializer 138 described above, the received data is outputtowards the liquid crystal unit 104 and the like. Additionally, theerror correction by the error pattern detection/correction unit 236 isperformed, assuming correction of an error of about one bit in atransmission frame. Thus, it is sufficient to perform this errorcorrection about one time for each transmission frame. In case thepattern of the coding rule violation is detected two times or more, theerrors are detected by the CRC check by the CRC check unit 238.

Heretofore, the functional configuration of the mobile terminal 200according to the present embodiment has been described. As describedabove, with the error pattern detection/correction unit 236 beingprovided, a transmission error can be corrected and the transmissionquality can be further improved. Furthermore, the error patterndetection/correction unit 236 only detects the coding rule violationbased on the amplitude pattern, selects a specific amplitude patternwhich will resolve the detected coding rule violation, and performs anerror correction corresponding to the amplitude pattern. Thus, nospecial error correction code has to be added at the transmitting unit202, and also, the circuit scale of the receiving unit 204 is barelyincreased.

(2-4: Error Correction Method)

Here, a supplementary explanation will be given for the error correctionmethod according to the present embodiment with reference to FIG. 13.FIG. 13 shows a method of error correction in relation to four amplitudepatterns which are coding rule violations. First, attention will befocused on an amplitude level pattern (3, −1) before correction, whichis a coding rule violation. In the case of this pattern, either theamplitude level 3 or −1 is an error.

However, as described above with reference to FIG. 10, the opening rateof the eye E1 between amplitude levels 3 and 2 is small compared to theeye E2 between amplitude levels 2 and 1. Thus, the possibility ofamplitude level 3 being mistaken for amplitude level 2 is higher thanthe possibility of amplitude level 1 being mistaken for amplitude level2 (the possibility of mistaking amplitude level −1 for amplitude level−2). Thus, if the pattern (3, −1), which is a coding rule violation, isdetected, the present embodiment presumes that the pattern is actually(2, −1), and corrects the corresponding decoded data to (0, 1).

For the same reason, when a pattern (−1, 3), which is a coding ruleviolation, is detected, it is presumed that the pattern is actually (−1,2), and the corresponding decoded data is corrected to (1, 0).Furthermore, when a pattern (1, −3), which is a coding rule violation,is detected, it is presumed that the pattern is actually (1, −2), andthe corresponding decoded data is corrected to (1, 0). Also, when apattern (−3, 1), which is a coding rule violation, is detected, it ispresumed that the pattern is actually (−2, 1), and the correspondingdecoded data is corrected to (0, 1). According to this configuration,one correction result can be uniquely specified from one error pattern,and processing burden for the error correction can be reduced.

Heretofore, the error correction method according to the presentembodiment has been described. In the explanation above, a multilevelcode for which the AMI code serves as a base has been consistently takenas an example for the sake of explanation. However, the applicationscope of the present embodiment is not limited to the AMI code, and itcan be applied to any code based on any coding scheme as long as awaveform having characteristics equivalent to those according to the newscheme can be formed. For example, it can be applied to a partialresponse code, a Coded Mark Inversion (CMI) code, and the like.

3: Modified Example

Here, a modified example according to the present embodiment will bedescribed. In the above explanation, a method of using correctionpatterns shown in FIG. 13 and performing the error correction on theamplitude level 3 or −3 of the multilevel code has been proposed as theerror correction method. However, depending on the circuit scale and theprocessing capacity of the receiving unit 204, it is sometimespreferable that the error correction is performed while taking intoconsideration other amplitude levels as well. As a matter of course, bytaking into consideration other amplitude levels as well, the errorcorrection ability is increased. Accordingly, the error correctionmethod to be used is to be selected as appropriate depending on the modeof the embodiment. Hereunder, a modified example configured to take intoconsideration other amplitude levels as well will be described.

(3-1: Functional Configuration of Mobile Terminal 200)

First, the functional configuration of the mobile terminal 200 will bedescribed with reference to FIG. 14. FIG. 14 is an explanatory diagramshowing a functional configuration example of the mobile terminal 200according to this modified example. Additionally, structural elementsthat have substantially the same function as those of the mobileterminal 200 shown in FIG. 12 are denoted with the same referencenumerals, and detailed explanation of these structural elements isomitted.

As shown in FIG. 14, the mobile terminal 200 is mainly configured fromthe transmitting unit 202 and the receiving unit 204. Furthermore, thetransmitting unit 202 and the receiving unit 204 are connected by thetransmission line 206. Furthermore, the transmitting unit 202 is mainlyprovided with the SYNC adding unit 212, the CRC adding unit 214 and theencoding unit 216. Accordingly, the functional configuration of thetransmitting unit 202 is substantially the same as that of the mobileterminal 200 shown in FIG. 12. Also, the receiving unit 204 is providedwith the decoding unit 232, the SYNC detection unit 234, the errorpattern detection/correction unit 236, CRC check units 252, 254, and adata selection unit 256.

First, a multilevel signal is transmitted to the receiving unit 204through the transmission line 206. When the multilevel signal reachesthe receiving unit 204, it is input to the decoding unit 232. Thedecoding unit 232 performs threshold determination by a comparator orthe like and detects the amplitude level of the multilevel signal.Furthermore, the decoding unit 232 decodes the 2-level transmission datafrom the data in the multilevel code based on the detected amplitudelevel. At this time, the decoding unit 232 converts from the data in themultilevel code to the data in the AMI code by using the coding ruleshown in FIG. 8, decodes the obtained data in the AMI code based on theAMI coding rule, and generates 2-level data corresponding to atransmission frame. The 2-level data generated at the decoding unit 232(hereinafter, decoded data) is input to the SYNC detection unit 234.

When the decoded data is input, the SYNC detection unit 234 detects thesynchronization code from the decoded data, and detects the beginningportion of the transmission frame. Then, the SYNC detection unit 234inputs to the decoding unit 232 the data and the CRC code following thesynchronization code. When the detection of the synchronization code bythe SYNC detection unit 234 is completed in this manner, the decodingunit 232 performs error correction on the input data. First, thedecoding unit 232 inputs the amplitude data of the multilevel code andthe decoded data to the error pattern detection/correction unit 236. Theerror pattern detection/correction unit 236 checks the amplitude patternof the multilevel code and detects the coding error violation. At thistime, the error pattern detection/correction unit 236 detects a portionwhere the amplitude pattern of consecutive two bits is any of (3, −1),(1, −3), (−1, 3) and (−3, 1).

When no coding rule violation is detected, the decoded data is input asit is to the CRC check unit 252 (#1) or the CRC check unit 254 (#2). Incontrast, if any of the amplitude patterns mentioned above is detected,the error pattern detection/correction unit 236 corrects the decodeddata based on correction rules (#1), (#2) shown in FIG. 15.

For example, when a pattern (3, −1) is detected, the error patterndetection/correction unit 236 presumes that the pattern of the correctamplitude level as a first candidate is (2, −1), and corrects thedecoded data of the corresponding bits to (0, 1) (#1). Then the errorpattern detection/correction unit 236 feeds back the decoded datacorrected based on (#1) to the decoding unit 232 as a decoded datacandidate (#1). Furthermore, the error pattern detection/correction unit236 presumes that the pattern of the correct amplitude level as a secondcandidate is (3, −2), and corrects the decoded data of the correspondingbits to (1, 0) (#2). Then the error pattern detection/correction unit236 feeds back the decoded data corrected based on (#2) to the decodingunit 232 as a decoded data candidate (#2).

Similarly, when a pattern (−1, 3) is detected, the error patterndetection/correction unit 236 presumes that the pattern of the correctamplitude level as a first candidate is (−1, 2), and corrects thedecoded data of the corresponding bits to (1, 0) (#1). Then the errorpattern detection/correction unit 236 feeds back the decoded datacorrected based on (#1) to the decoding unit 232 as a decoded datacandidate (#1). Furthermore, the error pattern detection/correction unit236 presumes that the pattern of the correct amplitude level as a secondcandidate is (−2, 3), and corrects the decoded data of the correspondingbits to (0, 1) (#2). Then the error pattern detection/correction unit236 feeds back the decoded data corrected based on (#2) to the decodingunit 232 as a decoded data candidate (#2).

Similarly, when a pattern (1, −3) is detected, the error patterndetection/correction unit 236 presumes that the pattern of the correctamplitude level as a first candidate is (1, −2), and corrects thedecoded data of the corresponding bits to (1, 0) (#1). Then the errorpattern detection/correction unit 236 feeds back the decoded datacorrected based on (#1) to the decoding unit 232 as a decoded datacandidate (#1). Furthermore, the error pattern detection/correction unit236 presumes that the pattern of the correct amplitude level as a secondcandidate is (2, −3), and corrects the decoded data of the correspondingbits to (0, 1) (#2). Then the error pattern detection/correction unit236 feeds back the decoded data corrected based on (#2) to the decodingunit 232 as a decoded data candidate (#2).

Similarly, when a pattern (−3, 1) is detected, the error patterndetection/correction unit 236 presumes that the pattern of the correctamplitude level as a first candidate is (−2, 1), and corrects thedecoded data of the corresponding bits to (0, 1) (#1). Then the errorpattern detection/correction unit 236 feeds back the decoded datacorrected based on (#1) to the decoding unit 232 as a decoded datacandidate (#1). Furthermore, the error pattern detection/correction unit236 presumes that the pattern of the correct amplitude level as a secondcandidate is (−3, 2), and corrects the decoded data of the correspondingbits to (1, 0) (#2). Then the error pattern detection/correction unit236 feeds back the decoded data corrected based on (#2) to the decodingunit 232 as a decoded data candidate (#2).

The decoding unit 232 inputs the decoded data corrected by the errorpattern detection/correction unit 236 and the CRC code to the CRC checkunits 252, 254. At this time, the decoding unit 232 inputs the decodeddata obtained from the error patter detection/correction unit 236 as thefirst candidate to the CRC check unit 252 (#1). Similarly, the decodingunit 232 inputs the decoded data obtained from the error patterndetection/correction unit 236 as the second candidate to the CRC checkunit 254 (#2). The CRC check units 252, 254 perform error check on thedecoded data based on the input CRC codes. The check results and thedecoded data output from the CRC check units 252, 254 are input to thedata selection unit 256.

When the check results are input from the CRC check units 252, 254, thedata selection unit 256 discards a decoded data candidate for which anerror is detected by a CRC check, and selects and outputs a correctdecoded data candidate. Additionally, in case both decoded datacandidates are confirmed to be errors by the CRC check, the dataselection unit 256 randomly selects a decoded data candidate and outputsthe same. The data output from the data selection unit 256 is output toother structural element. For example, when the transmitting unit 202corresponds to the serializer 134 described above and the receiving unit204 corresponds to the deserializer 138 described above, the receiveddata is output towards the liquid crystal unit 104 and the like.

Heretofore, the functional configuration of the mobile terminal 200according to a modified example of the present embodiment has beendescribed. As described above, in this modified example, the errorcorrection method to be performed by the error patterndetection/correction unit 236 is changed. Specifically, since errorcorrection is performed based on the table shown in FIG. 15, errorsoccurring at amplitude levels 1 and −1 can also be corrected. As aresult, the error correction ability can be increased compared to theerror correction method shown in FIG. 13.

4: Conclusion

Lastly, the functional configuration of the signal processing device ofthe present embodiment, and the effects obtained by the functionalconfiguration will be briefly summarized.

First, the functional configuration of the signal processing deviceaccording to the present embodiment can be expressed as follows. Thesignal processing device includes a signal receiving unit, an amplitudelevel detection unit, a violation detection unit, and an errorcorrection unit as described below.

The signal receiving unit mentioned above is for receiving a multilevelsignal having a signal waveform that is obtained by synchronously addingan encoded signal which is generated based on a specific coding rule anda clock which has an amplitude larger than the encoded signal and forwhich the transmission speed is half that of the encoded signal.

In this manner, the signal processing device receives a multilevelsignal by the above-described signal receiving unit. As described, themultilevel signal has a signal waveform that is obtained bysynchronously adding an encoded signal and a clock. When such signalwaveform that is obtained by synchronously adding a clock is used, theclock can be regenerated by detecting the polarity inversion cycle ofthe amplitude level. Accordingly, a PLL does not have to be provided atthe receiving side, and the amount of power consumption can be greatlyreduced. Also, a PLL does not have to be provided, and the circuit scalecan be reduced to that extent.

Also, the amplitude level detection unit mentioned above is fordetecting the amplitude level of the multilevel signal received by thesignal receiving unit.

The amplitude level of the above-described multilevel signal isdetermined based on a plurality of threshold levels that are set inadvance. At this time, an error may occur in the determination result ofthe amplitude level. As described above, the waveform of the amplitudelevel of the multilevel signal becomes thicker than for an encodedsignal on which a clock is not superimposed. Accordingly, a transmissionerror tends to occur for a high amplitude level in a transmission line.For this reason, in case of using the multilevel signal, an error tendsto occur in the determination result of the amplitude level by theamplitude level detection unit compared to a case where the encodedsignal is transmitted as it is. Thus, the above-described signalprocessing device has the violation detection unit and the errorcorrection unit which are described in the following.

The violation detection unit mentioned above is for detecting a bitposition at which rule violation of the specific coding rule occurred,based on a change pattern of the amplitude level detected by theamplitude level detection unit. Also, the error correction unitmentioned above is for correcting the detection value of the amplitudelevel corresponding to the bit position detected by the violationdetection unit so that the rule violation is resolved.

In this manner, by detecting the coding rule violation by referring tothe change pattern of the amplitude level, a position at which atransmission error occurred can be detected. Also, by correcting thedetection value of the amplitude level such that the coding ruleviolation is resolved, the transmission error can be corrected.Additionally, in case the transmission quality of the transmission linethrough which the multilevel signal is transmitted is relatively high,the proportion of error bits included in a received multilevel signal issmall. Accordingly, the transmission quality can be sufficientlyimproved by performing the error correction on the bit position at whichthe coding rule violation had occurred.

Furthermore, even if the error correction process at the signalprocessing device is added, the circuit scale is hardly increased. Thus,the technology is suitably used in a device for which it is desired touse a multilevel signal and to omit a PLL at the receiving side. Forexample, the technology relating to the above-described signalprocessing device is suitably used in a mobile phone, a portableinformation terminal, a portable game machine, a small notebook PC andthe like, and a small electronic device.

(Remarks)

The above-described receiving unit 204 is an example of the signalreceiving unit. Also, the above-described decoding unit 232 is anexample of the amplitude level detection unit. Also, the above-describederror pattern detection/correction unit 236 is an example of theviolation detection unit and the error correction unit.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2009-113892 filedin the Japan Patent Office on May 8, 2009, the entire content of whichis hereby incorporated by reference.

1. A signal processing device comprising: a wired interface that receives a multilevel signal having a signal waveform that is obtained by synchronously adding an encoded signal generated based on a specific coding rule and a clock which has an amplitude larger than the encoded signal and for which the transmission speed is half that of the encoded signal; and processing circuitry that detects an amplitude level of the multilevel signal received by the wired interface; detects a bit position at which rule violation of the specific coding rule occurred, based on a detected change pattern of the amplitude level; and corrects a detection value of the amplitude level corresponding to the detected bit position so that the rule violation is resolved.
 2. The signal processing device according to claim 1, wherein the processing circuitry corrects the detection value of the amplitude level corresponding to the detected bit position to an amplitude level adjacent to the detection value so that the rule violation is resolved.
 3. The signal processing device according to claim 2, wherein the multilevel signal has a signal waveform that is obtained by synchronously adding an encoded signal generated based on a specific bipolar coding rule and the clock.
 4. The signal processing device according to claim 3, wherein the wired interface receives a multilevel signal having a signal waveform which has six amplitude levels (A3, A2, A1, −A1, −A2, −A3; |A3|>|A2|>|A1|) and which is obtained by synchronously adding an encoded signal generated based on an AMI coding rule and the clock, and the processing circuitry recognizes a change pattern of amplitude levels of consecutive two bits changing from A3 to −A1 or from A1 to −A3 among detected amplitude levels from the multilevel signal received by the wired interface, and detects the recognized bit position as a bit position at which the rule violation occurred.
 5. The signal processing device according to claim 4, wherein the processing circuitry corrects, in case a change pattern of changing from A3 to −A1 is recognized, the detection value A3 of the amplitude level corresponding to the recognized bit position to A2 or corrects the detection value −A1 of the amplitude level to −A2, and corrects, in case a change pattern of changing from A1 to −A3 is recognized, the detection value A1 of the amplitude level corresponding to the recognized bit position to A2 or corrects the detection value −A3 of the amplitude level to −A2.
 6. The signal processing device according to claim 1, wherein the processing circuitry: decodes a bit sequence based on an amplitude level which has been corrected; performs error detection by using the bit sequence that has been decoded; decodes a bit sequence for each correction candidate, in case a plurality of correction candidates exist for the detection value of the amplitude level; and performs error detection for each decoding result to output a correct bit sequence.
 7. An error correction method comprising the steps of: receiving a multilevel signal having a signal waveform that is obtained by synchronously adding an encoded signal generated based on a specific coding rule and a clock which has an amplitude larger than the encoded signal and for which the transmission speed is half that of the encoded signal; detecting an amplitude level of the multilevel signal received in the step of receiving a signal; detecting a bit position at which rule violation of the specific coding rule occurred, based on a change pattern of the amplitude level detected in the step of detecting an amplitude level; and correcting a detection value of the amplitude level corresponding to the bit position detected in the step of detecting a violation so that the rule violation is resolved. 